2. Field of the Invention
The present invention relates to molded articles such as a carrier for electronic part, a heat-resistant tray for IC, etc. and liquid crystal polyester resin compositions capable of giving them.
2. Description of the Related Art
In carriers for transport of electronic parts, in particular, trays for transport of IC parts, there have heretofore been used vinyl chloride resins, polystyrene resins, polypropylene resins, etc. to which electroconductivity or antistatic properties have previously been imparted. On the other hand, if an electronic part, in particular, an IC part is wet when mounted on a printed circuit board or the like by soldering, water vapor is generated inside the IC by the heat of soldering, so that blisters or cracks are formed, resulting in breakage of the IC part. Therefore, water should be removed from the IC part at a temperature of 120.degree.-150.degree. C. before the mounting. In this drying step, it has been necessary to transfer the IC part from a transporting tray to an aluminum die-cast tray. However, trays usable both for the transport and for the drying have recently been produced from a modified polyphenylene ether resin to which electroconductivity or antistatic properties have been imparted, and they are coming into wide use.
In addition, there has recently been desired a tray which is usable both for the transport and for the drying and moreover has a high heat resistance which makes it possible to solder an IC part placed in the tray, without transferring the same. For example, development of such a tray by the use of a polyphenylene sulfide resin, a polyether ketone resin or the like as a base material is in progress. However, a product satisfactory with respect to warpage of molded article and moldability has not yet been obtained.
Liquid crystal polyester resins are generally called melt-type liquid crystal (thermotropic liquid crystal) polymers because of the following properties. Even when the resins are in a molten state, molecules of the resin do not entangle with one another because of their stiffness but form a polydomain in crystalline state, and under low shear stress, the resins behave so that the molecular chains are markedly oriented in the direction of flow of a melt. Because of this specific behavior, the liquid crystal polyester resins have a very excellent melt fluidity and depending on their structure, they are not deformed or foamed even at a soldering temperature of 260.degree. C. or higher. Therefore, it is considered that they are usable in a heat-resistant tray for IC when electroconductivity or antistatic properties are imparted to them. However, when the liquid crystal polyester resin is injection-molded, the resulting molded product shows marked orientation in the direction of flow of a melt (hereinafter referred to as MD in some cases). Therefore, the difference between shrinkage percentages in MD and the direction perpendicular to the flow (hereinafter referred to as TD in some cases) is very large, namely, the anisotropy is very remarkable. Accordingly, when the liquid crystal polyester resin is molded into a flat and relatively large product such as an IC tray, warpage has been liable to be caused and no satisfactory product has been obtainable.
It is known that the addition of talc is effective in reducing the anisotropy of the liquid crystal polyester and the warpage. For example, Japanese Patent Application Kokai No. 60-124649 relates to a composition suitable for ovenwares which comprises a blend of a fully aromatic polyester, talc and titanium oxide, and it discloses that the addition of talc reduces the anisotropy of molding shrinkage percentage. The addition of talc, however, deteriorates the mechanical strength greatly. In addition, this reference discloses that although not critical, the average particle size of the talc used is preferably 1 to 10 .mu.m.
Japanese Patent Application Kohyo No. 1-502833 relates to a composition comprising a blend of a fully aromatic polyester resin, a fibrous reinforcer component represented by glass fiber, and a filler component such as talc, and discloses that there can be obtained a product which shows only slight warpage and has a tensile strength of 10,000 pounds/inch square. But, this reference does not describe the kind of talc, its average particle size, the degree of reduction of warpage, etc.
Japanese Patent Application Kokai No. 4-13758 relates to a composition comprising a blend of a liquid crystal polyester having a melting point of 340.degree. C. or higher and talc having a specific surface area of 5 m.sup.2 /g or less and an average particle size of 40 .mu.m or less. By the use of such specified talc, hydrolysis during blending and heat deterioration can be markedly reduced, so that a composition excellent in strength and heat resistance can be obtained. This reference, however, does not describe the reduction of the anisotropy of a molded product and the reduction of warpage.
On the other hand, compositions comprising a liquid crystal polyester and electrically conductive carbon black are known as liquid crystal polyester resin compositions having electroconductivity or antistatic properties. In general, electrically conductive carbon black has a small particle size, a high porosity and a large specific surface area and exhibits electro-conductivity by forming a structure in a molten resin. It, however, is disadvantageous in that it greatly increases the melt viscosity of a melt. Even in the case of a liquid crystal polyester having a very low melt viscosity at molten state, when talc is blended for reducing the anisotropy and warpage of a molded product and electrically conductive carbon black is blended in such an amount that an electroconductivity required of an IC tray (a surface resistivity of 1.times.10.sup.4 to 1.times.10.sup.8 .OMEGA.) is attained, the resulting composition has a markedly increased melt viscosity and the thin portion of the molded product is not sufficiently filled with said composition. Furthermore, the impact strength is greatly decreased.
For the reasons described above, a molded article suitable as a carrier for electronic part, in particular, a heat-resistant tray for IC has not been obtainable merely by blending conventional talc and electrically conductive carbon black with a liquid crystal polyester having a high heat resistance in soldering.
The present invention is intended to provide a molded article such as a carrier for electronic part, a heat-resistant tray for IC, or the like, which has high heat resistance in soldering, only slight anisotropy and warpage, a surface resistivity of 1.times.10.sup.4 to 1.times.10.sup.8 .OMEGA., and an initial charged voltage due to electrification and a half-life period (a time required for the initial charged voltage due to electrification to be reduced to one-half) which are controlled to be further reduced; and a liquid crystal polyester resin composition excellent in moldability which gives said molded article.